The present invention relates to the field of software programmable robotic manipulators and assist devices, and in particular, robotic manipulators and assist devices that can directly interact with a human operator.
Various types of computer controlled machines have been developed in order to automatically perform or assist humans in performing routine or repetitive tasks. One class of devices developed for this purpose are computer controlled specialized machines that perform a particular task automatically. A specialized machine is a machine that is created for the purpose of performing a particular task, and which generally may not be reprogrammed or reconfigured to perform a substantially different task.
One example of a specialized machine is a computer controlled motorized arm that removes bottle caps from a conveyor belt and screws them onto bottles on another conveyor belt. Such a machine could have two axes of motion (also known as degrees of freedom). One would be a translational motion moving the cap from its location on one conveyor belt and positioning it over the bottle on another conveyor belt. The other would be a rotational motion that rotates the cap to engage it with the threads of the bottle. Each of these motions is driven by an actuator, such as an electric motor. Although this specialized machine may be controlled by software, the ability to reprogram the machine is very limited. For example, such a machine might be able to be reprogrammed to accommodate a different bottle having a different number of threads, or perhaps two different types of bottles on the same line. However, more complex modifications generally would not be permitted.
The major drawback to specialized machines as described above is their lack of programmability, which severely limits the range of tasks that they can perform. Not only can specialized machines not be reprogrammed to perform a different task, but, in fact, even modifications to the particular task they have been designed to perform may require hardware changes. For example, in the arm device described above, while the length of the arm's swing may be adjusted by software control to reach bottles at different positions on the conveyor belt, the device could not be merely reprogrammed to cope with bottles of different heights. To do so would necessitate a hardware change in order to add another translational axis of motion to allow vertical travel, resulting in three axes of motion rather than two. This lack of flexibility severely limits the utility of specialized machines.
Another type of computer controlled machine is a conventional robot. Unlike specialized machines, robots are designed to be adaptable to diverse tasks simply by reprogramming the robot. Consequently, robots generally have more mechanical flexibility so that they can be adapted to a number of different tasks. Generally, robots have one actuator, such as an electric motor or hydraulic cylinder, for each degree of freedom. The robot can perform tasks within an area known as its "workspace," which is defined as any volume of space that the robot can reach. Thus, robots are advantageous in that, unlike a specialized machine, they may be adapted to a variety of tasks by simply reprogramming the device.
Conventional robots, however, do not collaborate well with human workers. In fact, robots have been shown to be quite dangerous to the humans that must come into contact with them. For example, in a factory environment, a robot must often be designed to operate at high speed and to carry heavy payloads, requiring powerful actuators. Unfortunately, however, hardware and software errors may occur that cause the robot to malfunction. In such a case, the speed and power of the robot can have devastating consequences on anyone or anything in its vicinity. For example, a malfunction could cause the robot to move out of control and strike a nearby person with enough force to cause injury or death. Similarly, a robot might move a large piece of heavy machinery in an unpredictable direction, causing injury to persons or property. As a result of these dangers, people are normally excluded from the robot's workspace during its operation. In those instances where a person must be in the vicinity of the robot, such as medical applications, elaborate safeguards must be employed to slow the robot down or physically guard the person from unintended contact with the robot. This significantly reduces robots' ability to collaborate with a human. This is unfortunate, because collaboration between a robot and a human operator could relieve the human operator from the injurious physical requirements of a task, as well as providing the capability for computer control of the system.
Yet another disadvantage of conventional robots is that they often lack certain capabilities possessed by human workers. Such capabilities, which include human vision and tactile senses, allow human workers to cope with a much less structured environment than robots require. For example, in the bottle-capping example described above, a human worker can pick bottle caps out of a bin, while the robot requires the caps to arrive single-file so that they are at a predictable position for pick-up. In addition, a human worker can feel when a cap is cross-threaded, while a machine would not, except with the addition of considerable complexity. Similarly, human dexterity at assembling or joining workparts that do not quite fit or are not perfectly positioned is hard to duplicate mechanically. Instead, this situation must be avoided by more precise manufacturing of the parts themselves, at considerable additional expense. Moreover, the human ability to detect and deal with exceptional situations such as defective parts is also highly valuable. For all of these reasons, it is neither likely nor desirable that human workers will be removed from repetitive task environments and completely replaced by robots in the foreseeable future.
Another class of prior art devices are ergonomic assist devices designed to assist humans in performing a variety of tasks. These consist of primarily non-computerized, low-tech devices such as overhead rail systems, passive manipulator arms, or balancers. These devices perform functions such as counterbalancing loads against gravity (e.g., by use of a hoist), or lifting objects to an appropriate height to eliminate the need for an operator to bend over to manipulate a payload or workpiece (e.g. by use of a jack). Ergonomic assist devices have demonstrably improved the safety of numerous material handling operations, and are now widely found in production facilities, for example, in automobile assembly. It is not uncommon for a general assembly facility to employ hundreds of assist devices for lift assist alone. In addition, more complex assist devices that do more than counterbalance gravity are becoming increasingly prevalent in the automobile industry, and may be used for the installation of larger components such as cockpits, doors, seats, spare tires, exhaust pipes, driveshafts, radiators, and sunroofs.
While ergonomic assist device have proven valuable in manual handling, they have a number of drawbacks. One drawback is that they slow down the manual handling process due to the added inertia and friction of the assist device. For example, when moving a payload on an overhead rail or manipulator arm assist device, the operator must move not only the payload but also the assist device itself, which can be quite heavy. These problems are especially acute for more elaborate, and consequently heavier, devices. Assist devices do not provide any power assist or guidance that enables a human operator to overcome these inertial and frictional forces.
Another disadvantage of ergonomic assist devices are that they are not programmable and are typically customized to a particular task. For example, in the automobile industry, assist devices are typically customized to a particular body style and model. Thus, the life of a particular assist device may be limited to that of the production run, which may be only a few years. In contrast, programmable devices, like robots, can be reprogrammed to perform different tasks and thus can have a useful life far in excess of ergonomic assist devices.
Thus, in presently available devices, the need for ergonomic assistance, the need for freedom of motion desired by workers, and the need for software control of motion required by modern manufacturing practices, are conflicting requirements. Conventional assist devices for human workers are restrictive of their motion, and do not provide software control. Autonomous robots do not have the sensory capabilities or dexterity of human workers. Powered robots are considered unsafe for close association with humans. Thus, no one device meets all of these conflicting requirements.
In order to address some of these concerns, there have been a number of additional developments in recent years in the area of computer-controlled manipulators intended specifically for direct physical interaction with a human operator. These manipulators may be classified broadly as either active or passive. Active devices typically contain actuators at their joints and are capable of initiating motion. Passive devices, on the other hand, differ in that they cannot move without power input originating with the human operator. Unfortunately, none of these devices has proven successful in providing effective collaboration between machine and human.
Active computer controlled manipulators of this nature are generally known as "haptic interfaces." A haptic interface is a device which allows a human operator to touch, feel, and manipulate a computer simulation (also known as a "virtual environment"), or a remote manipulator. For example, in his dissertation"Virtual Fixtures: Perceptual Overlays Enhance Operator Performance in Telepresence Tasks," L. B. Rosenberg demonstrated that "haptic virtual fixtures," or hard walls that constrain motion to useful directions, can dramatically improve operator performance in teleoperation tasks such as remote peg-in-hole insertion. An example of a haptic interface is the "magic mouse" described by Kelley and Salcudean in their article "On the Development of a Force Feedback Mouse and its Integration Into a Graphical User Interface," International Mechanical Engineering Congress and Exposition, ASME, Chicago, Vol. DSC 55-1, pp. 287-94. This "magic mouse" is a computer interface device that can constrain an operator's hand to useful directions while interacting with a graphical user interface in order to avoid, for example, the cursor slipping off a pull-down menu.
Haptic displays have a number of significant drawbacks. One drawback is that haptic devices, being active, are capable of initiating motion and are therefore not as intrinsically safe as passive devices. Although this may not be a significant problem in small-scale desktop machines, it is a serious concern in large-scale machines, such as machines to assist an assembly line worker in manipulating parts weighing 20 to 500 pounds or more.
In addition to haptic displays, a number of passive computer-controlled manipulators have also been developed. One such device is a computer controlled manipulator with brakes rather than actuators at its joints, as disclosed in U.S. Pat. No. 5,201,772. This device also suffers from a number of disadvantages. One disadvantage is that such a device is not very flexible or successful at creating virtual walls or other surfaces. Because of the use of brakes at its actuators, this device can only effectively create virtual walls in certain directions. For example, it is very difficult to set up a curved virtual wall because the brakes used in the device can emulate the behavior of a wall only by dissipating energy in certain directions. Even if such a wall is set up, this dissipation of energy results in virtual walls that do not feel smooth but rather feel jagged or sticky.
Another similar device is described by M. Russo and A. Tadros in their article "Controlling Dissipative Magnetic Particle Brakes in Force Reflective Devices," ASME Winter Annual Meeting, Anaheim, Calif., pp. 63-70. This article describes a manipulator that includes both brakes and actuators at its joints. The actuators allow the device to improve upon the feel of a device based on brakes alone. On the other hand, because it is an active device, like a conventional robot, with actuators at its joints, it suffers from the disadvantages of such active devices described above.
Another similar device has been developed by R. A. Charles in his thesis, "The Development of the Passive Trajectory Enhancing Robot," at Georgia Institute of Technology. This device is based on the use of both brakes and clutches. Because clutches can transfer energy from one joint to another, the addition of clutches can potentially improve the feel of a virtual wall compared to a design based on brakes alone. This device is also disadvantageous, however, in that the number of clutches required can be quite large, and increases significantly as the degrees of freedom of the manipulator grow. Thus, non of these devices effectively allow collaboration between a human operator and a computer controlled manipulator without the dangers and disadvantages inherent in prior art robotic and mechanical assist devices.
Accordingly, it is an object of the invention to provide a device and method that will overcome the deficiencies found in the prior art.
It is another object of the invention to provide an assist device that can collaborate with a human operator without the dangers and limitations found in prior art robotic systems.
It is another object of the invention to provide an assist device that is computer controlled and can be reprogrammed to cope with different situations and/or tasks.
It is another object of the invention to provide an assist device that can compensate for any added friction and inertia caused by the assist device and its payload.
It is another object of the invention to provide an assist device that can direct the motion of a human operator and payload without the use of powerful actuators.
It is another object of the invention to provide a method for allowing a human operator to collaborate with an assist device without the deficiencies found in prior art robotic systems.